This invention relates to dual load type detonators, a method of manufacturing a dual load pellet in a single consolidation pressing operation, and a press used in accordance with the method. Dual load type detonators can be used in military, mining, automotive, and construction applications.
Detonators are typically used to detonate an explosive charge. Sometimes, initiators, such as exploding foil initiators, are used to set off the detonator. Many detonators require two explosive loads to meet certain design requirements. This is because some explosives, such as 2,2xe2x80x2,4,4xe2x80x2,6,6xe2x80x2-Hexanitrostilbene (HNS), are reliably initiated, but have a relatively weak output. Other types of explosives have a stronger output but are more difficult to reliably initiate. One example includes octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX).
Thus, some detonators include an initiating charge made of HNS which detonates a booster charge made of HMX. Since the powder used for the initiating charge is often relatively expensive, steps are taken to insure that only a minimum amount of this type powder is used.
In the prior art, such dual load detonators were fabricated by independently forming a pellet of HNS, independently forming a pellet of HMX, and then coupling the two pellets together using adhesives and/or mechanical fixtures.
In forming each pellet, controlling the density of the resulting pellet is critical. In a normal pressing operation, the required amount of explosive powder is weighed and placed into a pressing fixture. A high pressure of 1,000-30,000 lbs is applied to the fixture causing the compaction of the explosive powder. In some instances, the density is controlled by pressing to a specific pressure while in other instances the density is controlled by pressing a fixed amount of explosive into a known volume (also called pressing to a stop). Controlling the density is important because variations in density can cause variations in initiation sensitivity and in the output of the detonator.
In the prior art where each pellet is separately consolidated, controlling the density of each pellet can be a time consuming process. Moreover, it can be difficult to reliably couple the two pellets together.
It is an object of this invention to provide a less expensive dual load charge detonator by using only a minimum required amount of the expensive initiating charge powder.
It is a further object of this invention to provide a more robust charge wherein the initiating charge is in intimate contact with the booster charge.
It is a further object of this invention to eliminate the need for adhesives or mechanical fixtures previously used to couple two independently pressed pellets.
It is a further object of this invention to provide a method of simultaneously consolidating a dual load charge.
It is a further object of this invention to provide such a method which cuts the consolidation time in half by simultaneously consolidating both charges in a single consolidating pressing step.
It is a further object of this invention to provide a press for manufacturing a dual load charge in a single consolidation pressing operation.
The invention results from the realization that the expense associated with the initiating charge can be reduced, the time associated with separately consolidating the initiating charge and the booster charge can be cut in half, and that a more robust dual load pellet or charge can be manufactured by simultaneously consolidating both the booster charge and the initiating charge.
This invention features a method of manufacturing a dual load charge typically in a single consolidation pressing operation. The method comprises placing a first type explosive into a cavity to form a booster charge; forming a pocket in the booster charge; disposing a second type explosive in the pocket of the booster charge to form an initiating charge therein; and preferably simultaneously consolidating both the booster charge and the initiating charge thereby forming a dual load charge with intimate contact between the booster charge and the initiating charge.
In one example, the cavity is in a detonator housing (e.g. a transistor can) and the dual load charge is left in the cavity. In another example, the cavity is in a female mold member and the dual load charge is removed from the female mold member as a pellet. In the preferred embodiment, the first type explosive is octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine and the second type explosive is 2,2xe2x80x2,4,4xe2x80x2,6,6xe2x80x2-Hexanitrostilbene (HNS).
This invention also features a press for manufacturing a dual load charge preferrably in a single consolidation pressing operation. The press comprises an outer press having a working surface and a channel therethrough, the outer press receivable in a cavity; a first inner press receivable in the channel of the outer press, the first inner press having a working surface which extends beyond the working surface of the outer press; and a second inner press receivable in the channel of the outer press, the second inner press having a working surface which is flush with the working surface of the outer press.
In the preferred embodiment, the outer press further includes a funnel-shaped portion in communication with the channel for loading the cavity with an explosive through the channel when the outer press is placed in the channel.
The preferred method of manufacturing a dual load pellet in a single consolidation pressing operation, in accordance with this invention includes placing a first type explosive in a cavity to form a booster charge and then forming a pocket in the booster charge. The pocket is formed by disposing an outer press having a working surface and a channel therethrough in the cavity in combination with a first inner press receivable in the outer press. The first inner press has a working surface which extends beyond the working surface of the outer press in order to form the pocket. Then, a second type explosive is disposed in the pocket to form an initiating charge. In this step, the first inner press is removed and the second type explosive is poured into the channel of the outer press. Finally, a second inner press is placed in the channel of the outer press. The second inner press has a working surface which is flush with the working surface of the outer press. By applying pressure to the second inner press, both the booster charge and the initiating charge are simultaneously consolidated thereby forming a dual load pellet with intimate contact between the booster charge and the initiating charge.